In general, the surface of a solid such as a metal and a polymer has an inherent surface energy, and the surface energy can be evaluated by measuring the contact angle.
On the surface of the solid, when a straight line is drawn from a point where a liquid in a stationary state is brought into contact with the solid to the liquid surface, an angle with respect to the surface of the solid refers to a contact angle (θ). When the contact angle (θ) is small, spherical water bubbles wet the surface of the solid while losing the form thereof on the solid surface, and in this case, the surface of the solid is said to have hydrophilicity. Conversely, when the contact angle (θ) is large, the liquid does not wet the surface of the solid while maintaining a spherical shape and thus is said to have hydrophobicity.
Aluminum is a lightweight metal diversely and frequently used in various fields, and there is a lot of need for imparting hydrophobicity to the surface of aluminum.
However, technologies in the related art have a problem in that the procedure is very complicated because a separate coating agent is used or a chemical solution is used.